Work done for other people or for God and the worship of God. Jacob worked for Laban seven years for each of his wives (Gen 29:15-30). Service could be slave labor (Exod 5:11; Lev 25:39; 1 Kings 12:4; Isa 14:3 cp Lam 1:3), farm work (1 Chron 27:26), or daily labor on the job (Psa 104:23). It could be service of earthly kingdoms (2 Chron 12:8; cp 1 Chron 26:30), of God’s place of worship (Exod 20:16; cp Num 4:47; 1 Chron 23:24), of God’s ministers (Ezra 8:20), and of God (Josh 22:27). Not only people do service; God also done service (Isa 28:21). Even righteousness has a service (Isa 32:17).
Having the key to something denotes power and authority. You have the right to enter in and the right to refuse entry to others. In the ancient world, keys were given to the steward, a servant whom the master of the house trusted to care for the household. The long, large keys of the day were often carried on a person’s shoulder.